The present invention relates generally to heat pumps, air conditioning and refrigeration equipment. More specifically, the invention relates to a control system for regulating the flow of refrigerant in a system having a variable capacity or variable speed compressor.
The Applicants' assignee has developed a control system for heat pumps that has a decoupled sensor arrangement in which refrigerant is metered through the refrigeration system, based on compressor discharge temperature and ambient air temperature measurements. The sensors are decoupled in that the ambient air temperature and compressor discharge temperature are largely independent of one another. For further information, see U.S. Pat. No. 5,311,748 to Bahel et al., entitled "Control System for Heat Pump Having Decoupled Sensor Arrangement," issued May 17, 1994.
The Applicants' assignee has also developed a control system in which the indoor airflow rate is controlled by a humidity-responsive adjustable speed fan. The control system strives to select the fan speed for optimal operating efficiency and improved occupant comfort. For further details see U.S. Pat. No. 5,303,561 to Bahel et al. entitled "Control System for Heat Pump Having Humidity Responsive Variable Speed Fan," issued Apr. 19, 1994.
The Applicants' assignee has also developed a refrigerant charge detection system or diagnostic system that detects improper amounts of refrigerant (overcharge and undercharge). For further details see U.S. patent application Ser. No. 08/095,897 to Bahel et al. entitled "Overcharge--Undercharge Diagnostic System for Air-Conditioner Controller," filed Jul. 21, 1993.
Industry demand for improved efficiency has caused many heating and cooling system developers to experiment with variable speed compressors and variable capacity systems. In a variable speed or variable capacity system refrigerant flow is controlled, at least in part, by changing the speed at which the compressor operates. Contrast this with fixed speed or fixed capacity systems in which refrigerant flow is regulated only by an adjustable restricted orifice, such as an electrically adjustable expansion valve.
The present invention strives to integrate the advantages of Applicant's assignee's prior systems with the advantages of variable speed and variable capacity systems. According to one aspect of the Applicant's invention, the expansion valve is controlled based on ambient air temperature and compressor discharge temperature measurements, taking into account the current operating capacity of the compressor. The operating capacity of the compressor is, in turn, dynamically controlled based on indoor ambient temperature and based on the load or demand that is dictated by the thermostat setpoint.
According to another aspect of the invention the speed of the indoor fan or blower is adjusted based on outdoor ambient temperature measurements, taking into account the current operating capacity of the compressor.
In yet another aspect of the invention a charge detection diagnostic system evaluates whether the system is overcharged or undercharged, based on outdoor ambient temperature and compressor discharge temperature measurements, taking into account the current operating capacity of the compressor. The diagnostic system automatically controls the expansion valve setting prior to making the charge detection decision. The current compressor capacity dictates which of a series of discharge temperature/outdoor temperature relationships is used to make the charge detection decision.